The hamstrings as a muscle group cross both the hip joint and the knee joint and are one of the most critical muscles used for locomotion (walking/running). The biomechanics of the hamstrings are such that they create tremendous amounts of force for both hip extension and knee flexion. In fact, they are unique in that they are one of the only muscle groups in the human body that cross two joints and are classified as primary movers for both joints. Usually the mechanics of a two joint muscle are such that there is greater leverage at one joint over the other and the actions of the muscle are thus classified as primary (stronger of the two actions) and secondary (weaker of the two actions). For example, the calf muscle (gastrocnemius) crosses both the knee joint and the ankle joint and is considered a primary ankle flexor and a secondary knee flexor. This means that the calf generates significantly more force at the ankle then at the knee and as such it is best strengthened by exercises that focus on creating resistance for ankle flexion versus knee flexion. The fact that the hamstrings generate equivalent forces at both the hip and the knee makes it one of the most challenging muscle groups to isolate for strength training in the body. The current methodology for equipment design is to determine a muscle's primary action, stabilize the body for that action, and then provide adequate resistance to the muscle during that action. This works extremely well with muscles that have only one primary action like the calf (e.g. using a heel raise machine). However, with the hamstrings, which have dual primary actions, engineers have erroneously created equipment that attempts to isolate one action from the other. As such we see machines like the Seated or Prone Hamstring Curl Machine for knee flexion, and the Donkey Kick Machine for hip extension which are well known in the industry. In these current designs an improper understanding of the biomechanics of the hamstrings has led to poor ergonomics and an inability to maximize strengthening of the hamstrings muscle group.